Movies: Fox is worried about the X-Factor: Will the series' true believers be the only ones in line when the feature opens?

As 20th Century Fox prepares for the June 19 opening of its feature-length sci-fi thriller based on the popular television series "The X-Files," the studio faces a daunting task: Can it attract moviegoers who know little or nothing about the long-running TV show?

From the outset, Fox executives knew they could count on the show's built-in core audience to jam the turnstiles once the movie comes out. Between 20 million and 30 million viewers tune in Sunday nights to follow FBI agents Mulder and Scully as they investigate vampire murders, alien abductions, government conspiracies and even seemingly ordinary people who become monsters.

The most ardent of these fans--who are dubbed "X-Philes"--hang on every bizarre plot twist and character nuance contrived by creator-executive producer Chris Carter, whether it's pondering the identity of Cigarette-Smoking Man or waiting to see if agents Fox Mulder (David Duchovny) and Dana Scully (Gillian Anderson) ever kiss.

Fox reasons that if even 20 million viewers turn out to see the film, the studio and exhibitors would reap about $100 million in ticket sales.

Some see "The X-Files" as a unique case in which a movie studio has joined forces with its corporate television arm to exploit a popular TV show. By injecting it with $66 million, bigger and louder special effects and a grander canvas upon which the two investigators can determine whether "the truth is out there," producers hope to attract the truly loyal as well as the clueless.

But not only do the producers of the film have to overcome some perceptions that the film may be little more than a big-screen episode of the series, they must also combat the problems that have plagued other television shows that have been unsuccessfully turned into movies.

"Yes, it was a calculated risk," Carter acknowledged. "I didn't want to do anything that would tarnish the series. But I also saw it as an opportunity, if we got the budget and took the right approach, to do an event that could stand on its own but also could help the series coming back in year six."

Tom Rothman, Fox's production chief, added: "The challenge is to make a movie that satisfies fans and challenges people who don't know about it. It's not an easy stew. But 'The X-Files' is not an easy series. It's not easy television. It's exciting and different. That's what people look for."

The "X-Files" film is the latest in the rush to turn hit television shows into films--a trend that has met with mixed response at best.

The "Star Trek" movies, "Mission: Impossible," "The Brady Bunch Movie," "The Fugitive" and "The Naked Gun" (a big-screen adaptation of the failed "Police Squad" series) were solid hits with filmgoers. But these films were made years after the original series went off the air, and their success was based largely on nostalgia.

But the TV-to-film graveyard is also littered with films that stumbled from the small screen to the cinema. They include "The Beverly Hillbillies," "Leave It to Beaver," "Sgt. Bilko," "Mr. Magoo," "The Saint" and last year's version of the '60s sitcom "McHale's Navy."

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In the case of "The X-Files," the series is at the height of its popularity. More important, the movie marks perhaps the first time since the 1960s that a major feature film has been produced of a series that is still going strong.

Fox Entertainment Group President Peter Roth, who developed the "X-Files" series more than five years ago when he was head of 20th Century Fox Television, said, "When you have a show working in whatever medium, you're hard pressed to chance going out of that medium to replicate the same success. It's the danger in trying to remake a classic--it could be poorly compared to the original."

But Roth called "The X-Files" film "a beautifully notable exception" to the dangers of movie adaptations.

"It will work because of the storytelling and brilliance of Chris Carter," said Roth, who has not seen the film.

And Carter, who wrote the film and is one of its producers, said that he did not feel that the uninitiated would turn away from checking out the movie.

"I think people will go unless they have a real resistance," he said. "When I stand in a movie line on a Friday or Saturday night, I want to see a good movie."

Carter has long maintained that the film would deal with major questions left dangling during the show's five-year run. In addition to attracting all audiences, he said he wanted to reward hard-core fans of the series who had stayed loyal through its run.

Among the most puzzling questions of the series: Is the Cigarette-Smoking Man Mulder's father? What ever happened to Mulder's sister, who was abducted by aliens? Who abducted Scully and what happened to her? What happened to the child she apparently bore?